SADD and SREM for membership in Redis

Introduction

SADD adds items to a group without duplicates. SREM removes items from that group. This helps keep track of unique members easily.

When you want to keep a list of unique users who liked a post.

When you need to add or remove tags from a set of tags for an article.

When tracking online users joining or leaving a chat room.

When managing a list of unique product IDs in a shopping cart.

Syntax

Redis

SADD key member [member ...]
SREM key member [member ...]

SADD adds one or more members to the set stored at key.

SREM removes one or more members from the set stored at key.

Examples

Adds 'apple', 'banana', and 'cherry' to the set named 'myset'.

Redis

SADD myset apple banana cherry

Removes 'banana' from the set named 'myset'.

Redis

SREM myset banana

Adds two users to the 'users' set.

Redis

SADD users online_user1 online_user2

Removes 'online_user1' from the 'users' set.

Redis

SREM users online_user1

Sample Program

First, add three fruits to the set 'fruits'. Then remove 'banana'. Finally, get all members of 'fruits'.

Redis

SADD fruits apple banana cherry
SREM fruits banana
SMEMBERS fruits

Important Notes

SADD returns the number of elements actually added (ignores duplicates).

SREM returns the number of elements actually removed (ignores missing members).

Sets in Redis do not allow duplicate members.

Summary

Use SADD to add unique members to a set.

Use SREM to remove members from a set.

Sets help manage collections of unique items efficiently.